1. Field of Invention
The invention relates to crankshaft position sensing devices and methods of generating engine timing signals.
2. Description of the Prior Art
A crankshaft position responsive device is an essential element in any ignition timing system, engine cylinder firing system or synchronization system. In many engines, a distributor provides indirect crankshaft information such as engine speed and also distributes the spark to the proper cylinder at an instant when the piston of each cylinder is at a preferred position within its power cycle. Distributors are often driven through a worm gear by a camshaft which in turn is driven by an engine crankshaft. Significant problems do exist in present distributor systems. One source of error arises due to a stackup of tolerances (machining inaccuracies) between the crankshaft-worm gear-distributor cam making precise and repeatable engine synchronization difficult. Dynamic errors are especially evident during periods of acceleration and deceleration during which time imperfections in the gearing such as backlash become more apparent.
A second problem resulting in a constant position offset error arises because crankshaft position is not measured directly but is obtained by measuring the motion of intermediate elements such as a timing gear or vibration damper which can be misaligned relative to the crankshaft. Misalignment may result because of the imprecision in slots, or in keys and keyways that are used to position these intermediate members to the crankshaft.
To eliminate the buildup of mechanical errors due to gearing inaccuracies, systems have employed a sensor mounted proximate to the crankshaft at the front of engine. Such a sensor could be a reluctance sensing device responding to the passage of sense features such as protrusions or holes on a nearby sense wheel which is attached to the crankshaft vibration damper or timing gear
A front mounted crankshaft sensor is susceptible to many sources of error. As an example, it must operate in a hostile exposed environment at the front of the engine. Furthermore, the front mounting, because of its easy accessibility, encourages user tampering. Permitting access to critical ignition components may give the user the opportunity to "fine tune" the performance of his vehicle; however, it is also possible for the user to circumvent the manufacturer's complex ignition timing synchronization which may be necessary to meet legislative standards for minimizing automotive exhaust emissions.
Due to the nature of the automotive market, it is desirable to produce a low cost crankshaft sensing and positioning device which is readily adaptable to most domestic and foreign engines. An advantage of the present invention is that it cooperates with existing engines and engine components so that integration of the crankshaft sensor into the engine is accomplished with a minimum of engine design changes.
It was determined that the rear of most engines are similar. In particular, the bottom rear of many cylinder blocks near the oil pan and within the transmission dust cover affords an accurately machined surface into which a crankshaft sensing element could be mounted with engine design changes, limited for the most part to making provision for sensor fastening holes in the bottom of the cylinder block and minor machining of the crankshaft flange, to the transmission dust cover and flywheel (or flex plate).
Improvements in engine performance such as fuel economy and emissions control require repeatable cycle-to-cycle crankshaft position and speed information. This is accomplished by the present invention. A further advantage of the present invention is that its output or timing signal is not effected by acceleration or deceleration of engine components or by mechanical wear.
It is an object of this invention to provide an improved crankshaft position sensor. It is a further object to accurately measure engine speed and to generate accurate spark timing information. Still a further object of this invention is to inhibit user tampering with the manufacturer specified engine timing while still affording a limited range of adjustability so that the basic ignition timing can be varied in order to compensate for ignition timing changes due to mechanical wear of engine components. It is a further object to monitor crankshaft position directly.